public class Circle {
   private double radius;
   public Circle(){}
   public Circle(double radius){
       this.radius=radius;
   }
   public void setRadius(double radius){
       this.radius=radius;
   }
   public double getRadius(){
       return radius;
   }
   public void showCircumference(){
       double circumference= 2 *Math.PI*radius;
       System.out.printf("圆的周长为：%.2f\n",circumference);
   }
   public void showArea(){
       double area=Math.PI*radius*radius;
       System.out.printf("圆的面积为：%.2f\n",area);
   }
   public static void main(String[] args){
       Circle circle=new Circle(5.0);
       circle.showCircumference();
       circle.showArea();
   }
}
